HYDROLYTIC ENZYMATIC-ACTIVITY IN DEEP-SEA SEDIMENTS

Hydrolytic activities of five enzymes were measured in deep-sea sedime nt cores at three stations under in situ temperature and pressure in t he NE-Atlantic in March/April and July/August 1992. Generally, activit y profiles declined vertically in the upper 10 cm of the cores. Experi ments under in situ pressure were not significantly different from mea surements under surface conditions. The ranking of potential activity rates in the top sediment horizon was: aminopeptidase > esterase > chi tobiase > beta-glucosidase > alpha-glucosidase with ratios of 687/174/ 11/3/1. This is similar to ratios obtained in marine aggregates from t he upper mixed layer, thus supporting the idea of pelagic-benthic coup ling in the open ocean. The vertical activity profiles show that the b iochemical composition, and thereby the nutritive quality of the degra dable material, changed with depth in the sediment cores. About 518 mg carbon was potentially mobilized in the 0-1 cm sediment horizon per s quare meter per day. This contrasts with the input of particulate orga nic carbon to the sea floor in this area of only 2.74 mg C m(2) d(-1), determined by sediment traps, which indicates that the deep-sea benth ic community can rapidly utilize sedimenting particulate organic mater ial and highlights the importance of extracellular enzyme activity in the sediment biogeochemical loop.